A door of an office building, a tenant building, an apartment building, or the like is generally, for earthquake-proofing purposes, mounted to a wall having a wall opening formed therein to which a door frame structure made of steel with a certain rigidity is mounted, and supported by the door frame structure pivotably about one vertical side of the door.
Such a door frame structure includes a pair of left and right vertical frame members and a cross frame member joining upper portions of the vertical frame members, and is an inverted U-shape as a whole, and each frame member is firmly attached to a bed curing material (post) defining a wall opening by a known fixing means such as welding, adhesion, and caulking, etc.
However, in a case where a door frame structure is firmly mounted to a wall or the like in which a wall opening is formed, when lateral vibration occurs due to an earthquake, etc., relative story displacement of a skeleton such as a wall, etc., may occur, and following this relative story displacement, the door frame structure plastically deforms into a diamond shape, and may result in a situation where the door cannot be opened and closed and trap an inhabitant inside the building.
To address such a problem, Patent Literature 1 discloses a door frame structure that releases a door even when the door frame structure deforms following relative story displacement of a skeleton caused by an earthquake and the door and the door frame structure coming into contact with each other.
In detail, as shown in FIG. 9, a door frame structure 101 includes two frame members 102 and 103 that are folded. The frame members 102 and 103 are movable frame members coupled so as to be mutually movable toward the inside of the door frame structure 101.
In addition, between the frame members 102 and 103, a coil spring 104 elastically deformable in the up-down direction, plastically supports the frame members 102 and 103.
In such a state, for example, when an earthquake occurs and a skeleton (not shown) greatly oscillates, according to relative story displacement of the skeleton, the door frame structure 101 also plastically deforms, and the door frame structure 101 comes into contact with an outer edge of a door 105. Then, due to permanent deformation of the door frame structure 101 after earthquake vibration stops, the door frame structure 101 and the door 105 come into contact with each other.
However, if contact pressure between the door frame structure 101 and the door 105 exceeds a predetermined pressure, the coil spring 104 interposed between the frame members 102 and 103 absorbs the contact pressure between the door frame structure 101 and the door 105. Further, the frame members 102 and 103 are mutually movable toward the inside of the door frame structure 101, so that the door frame structure 101 itself absorbs the contact pressure.
Therefore, even if the door frame structure 101 and the door 105 come into contact with each other due to an earthquake, the door 105 can be opened and emergency evacuation is enabled.